1. Field of the Invention
This invention relates generally to well pump equipment and more particularly to an apparatus for preventing gas locks in traveling piston-type well pumps.
2. Description of Related Art
When there is insufficient reservoir pressure in an oil well to overcome the hydrostatic head of the fluid in the well pipe, the oil and other fluids in the well cannot flow unaided to the surface for collection. In such wells, the fluid must be mechanically assisted or pumped to the surface. A variety of pumps, gas lift apparatus, and other devices exist for this purpose, but among the oldest, and yet most common and popular apparatus used are the stroking or traveling piston-type well pumps. These pumps typically have a standing one-way check valve positioned on the bottom of a string of tubing pipe in the liquid fluid near the bottom of the well, a traveling piston in a hollow cylindrical barrel just over the standing valve with a traveling one-way check valve in the piston, a sucker rod or pump rod extending from the piston to the well head on the surface of the ground, and a pump jack actuator or driver on the ground surface connected to the sucker rod for reciprocating the piston and traveling valve up and down in the well. The most common pump jack actuators or drivers are characterized by a pivoted rocking beam driven by a rotating crank shaft-type mechanism, although other actuators, such as hydraulic cylinder-driven pump jack apparatus, are also used.
These traveling piston-type pumps operate by drawing the piston upwardly, which results in drawing or sucking the fluid through the standing valve into the barrel. Then, the stroke is reversed so that the piston travels downwardly. During the downstroke, the standing valve closes to prevent fluid in the cylinder barrel from being pushed by the piston back into the well casing or back into the reservoir formation. At the same time, the traveling valve opens to allow the fluid above the standing valve to flow through the piston to a position in the cylinder barrel above the piston.
On the next upstroke, as the standing valve is opened to draw more fluid into the cylinder barrel under the piston, the traveling valve in the piston is closed to prevent the fluid above the piston from flowing back through the piston. In this manner, each successive stroke cycle of the piston draws more fluid from the formation to a position above the piston so that the fluid is pumped to the surface of the well where it can be collected for processing or sale.
Some of the reasons that the traveling piston-type pump has remained popular and effective over the years are that the mechanism is simple and the pump is usually reliable and easy to use. However, there are situations in which this kind of pump is not efficient or effective. For example, wells in reservoirs that produce excessive compressible fluids, such as natural gas, along with the noncompressible liquids, such as oil and water, tend to cause problems for this kind of pump.
The gas is easily drawn through the standing valve into the cylinder barrel on the piston upstroke. However, on the downstroke, when the standing valve is closed and the noncompressible liquid is normally expected to force the traveling valve open, gas between the traveling valve and the standing valve will compress, thereby allowing the hydrostatic head of the fluid above the traveling valve to keep the traveling valve from opening. Yet, on the upstroke, the gas and liquid above the standing valve prevent any more fluid from being drawn into the cylinder barrel, since the compressed gas merely expands to fill the expanding space between the standing and traveling valves. Consequently, the upstrokes and downstrokes of the pump cycles simply continue to alternately compress and expand the gas caught between the standing valve and the traveling valve without pumping any liquid. This condition is known as "gas lock" and prevents the pump from performing its intended function, i.e., pumping fluid in the well to the surface.
If there are sufficient quantities and pressure of gas in the reservoir, other apparatus are available for lifting fluids to the surface, such as gas lift, gas-driven pig devices, and the like. However, where there is enough gas in the well to gas-lock a traveling piston-type pump, yet not enough gas or pressure to drive other gas-powered lift mechanisms, a continuing problem has existed in recovering fluids from wells.
There have been other attempts to solve such gas-lock problems in traveling piston-type pumps. For example, the device in the U.S. Pat. No. 3,139,039, issued to E. Adams in 1964, was specifically intended to solve the problem of gas locks in a traveling piston oil well pumps. Adams coupled the traveling valve closure ball by an elongated rod to a secondary piston that frictionally engages the sides of the barrel to open the traveling valve. Sizing and placement of the components, however, still allows gas compression and decompression during the downstroke and upstroke. The Adams patent disclosure seems to identify the failure to pump oil in gassy fields as one of gas pressure in the tubing over the traveling valve, which is a different theory of the source of the problem than the explanation of the gas lock problem as I have described, and it attempts to solve the problem in a different way. Moreover, the frictional drag between the piston and the working barrel increases the load on the sucker rod, the motor, and the associated pump jack drive mechanism, gear box, and the like. Furthermore, over a period of time as the device is used, wear on the secondary piston changes its frictional drag causing unseating force on the valve closure to decrease and adversely affecting the pump jack counterbalance adjustments, thereby rendering the pump's operation uncertain and unreliable. Also, the apparatus disclosed by Adams does not permit free rotation of a ball valve closure on all axes, so it tends to wear faster and
unevenly
The U.S. Pat. No. 2,214,956, issued to W. Dunlap in 1940 uses a rod attached at the top end to the traveling valve closure member, while the bottom end of the rod frictionally slides through the standing valve closure member to urge the standing valve open and closed. Dunlap's attempted solution focused on what was apparently thought to be excessive gas pressure under the standing valve instead of between the standing valve and the traveling valve.
The U.S. Pat. No. 2,528,833, issued to K. Kelley in 1950 is also directed to an attempt to minimize the gas lock problem by reducing the space between the standing valve and the traveling valve. U.S. Pat. Nos. 1,184,018 granted to Rathbun in 1916, and the 3,215,085, issued to Goostree in 1965 both employ operating mechanisms somewhat similar to that of the current invention. These early inventions advanced the state of the art at that time. However, experience has shown that in order to achieve dependable, efficient gas lock breaking or prevention, additional improvements still were necessary. Even where gas lock breakage is partially effective, it is often necessary to operate pumps at speeds faster or slower than the natural flow rate of fluid from the reservoir. Such circumstances usually result in substantially decreased production from the well, and, in many instances, production is not even economically feasible at all.
Consequently, prior to this invention, there still remained a need to improve on the various previous attempts to solve the gas lock problem. With the current invention under test in approximately 1000 gassy wells, production from these wells has on the average doubled. The reason for the increased production is because the present invention is more highly effective and efficient at breaking and effectively eliminating gas locks, and, as a result, it permits pumping at optimum speed for fluid production from the reservoir of any given well, rather than at the inefficient speeds necessary in other designs to break gas locks.